With recent technological advancements in computer and wireless communications, mobile wireless computing has seen increasingly widespread use and application. Not constrained by wires, users with mobile computing devices can move around freely at their convenience, and may often need to communicate with each other in circumstances where there is no fixed infrastructure. In such cases, they can form a mobile ad hoc network (MANET) or mobile wireless mesh network. A mobile wireless mesh network is an autonomous system of wireless mobile routers (and associated hosts), which can move randomly and re-organize themselves into an arbitrary network without any underlying backbone and infrastructure.
Besides mobile wireless mesh networks, recently, interesting commercial applications of fixed wireless mesh networks have also emerged. One example of such a commercial application is “community wireless networks,” which are used to provide broadband Internet access to communities that previously did not have such access. In these fixed “community wireless networks”, each wireless router in the network not only provides Internet access for attached users but also becomes part of the network infrastructure and can route data through the wireless mesh network to its destination. A routed wireless mesh network is highly flexible and inherently fault-tolerant. It simplifies line-of-sight problems and extends the reach and coverage of the network with a minimal amount of network infrastructure and interconnection costs.
There are also hybrid wireless mesh networks where some mesh routers are mobile and the others are not. In whatever cases (whether mobile or fixed or hybrid), wireless mesh networks have some salient characteristics, such as: highly dynamic, autonomous, peer-to-peer, multi-hop, often limited bandwidth and computing power etc. The wireless mesh networks are highly dynamic for two reasons: First, the routers themselves may move (e.g. in mobile or hybrid wireless mesh networks), causing fast topological changes. Second, even if the routers themselves do not move (e.g. in fixed wireless mesh networks), the radio link qualities can change very quickly because of interference, geographical and environmental factors etc. The traditional routing protocols (e.g. OSPF, RIP), designed for wired infrastructures, can not handle such fast changes. Many of the ad hoc routing protocols (e.g. AODV), on the other hand, lack the ability to flexibly adapt to the radio link quality changes.
Routing protocols have traditionally focused on finding paths with minimum hop count. However, such paths can include slow or lossy links, leading to poor throughput. These lossy links are bad enough to impair packet forwarding performance, but not so bad as to prevent routing protocol from using these links to forward traffic.